<template>
  <ul class="list">
    <li
      class="item"
      v-for="item of letters" :key="item" :ref="item"
      @click="handleLetterClick"
      @touchstart="handleTouchStart"
      @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
    >{{ item }}</li>
  </ul>
</template>

<script>
export default {
  name: 'Alphabet',
  props: {
    cities: Object
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      time: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.time) {
          clearTimeout(this.time)
        }
        this.time = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
  @import "~styles/variable.styl"
 .list
   position: absolute
   display:flex
   flex-direction column
   justify-content:center
   top:1.58rem
   right:0
   bottom:0
   width:.4rem
  .item
    line-height:0.4rem
    color: $bgColor
    text-align:center
</style>
